1. The Field of the Invention
The present invention relates to modular bone fixation plate assemblies and, more specifically, modular spinal plate assemblies used for securing together adjacent vertebrae of the spine.
2. The Relevant Technology
Bone fixation plate assemblies are used for securing together adjacent bones or bone segments. For example, bone fixation plate assemblies are commonly used for securing together adjacent vertebra of the spine when it is desired to fuse the vertebra together. U.S. Pat. No. 6,402,756 discloses one type of bone fixation plate assembly. As depicted in FIG. 1, the plate assembly 9 includes a first plate 1A having a first pair of through holes 2A and 2B for receiving bone screws and a pair of prongs 3A and 3B. A threaded bore 4 is formed at the intersection between prongs 3A and 3B and is configured to receive a set screw (not shown). Plate assembly 9 also includes a second plate 1B that has a second pair of through holes 4A and 4B for receiving bone screws and an end face with an elongated bore 5 formed therein and configured to receive the pair of prongs 3A and 3B. An opening 6 is formed on a top surface of second plate 1B so that when prongs 3A and 3B are received within bore 5, threaded bore 4 can be accessed through opening 6.
During use, prongs 3A and 3B are slidably received within bore 5 and are advanced or retracted therein until plate assembly 9 achieves a desired length for mounting on adjacent bones. The set screw is then threaded into threaded bore 4 through opening 6. As set screw is screwed into threaded bore 4, prongs 3A and 3B are pushed apart so as to bias against the interior surface of second plate 1B, thereby securing first plate 1A to second plate 1B by frictional engagement. Plate assembly 9 can then be placed to span between two bones and the bone screws can be passed through holes 2A, 2B and 4A, 4B and into the bones so that plate assembly 9 is secured to the adjacent bones.
Although plate assembly 9 is functional, it has a number of shortcomings. For example, plate assembly 9 can only be used for securing two adjacent bones together. It is common, however, to fuse together three or more consecutive vertebra. In that case two or more separate plate assemblies 9 is required where the end of two separate plate assemblies needs to be screwed into the same vertebra. Attaching multiple separate plates is labor intensive and time consuming. It addition, it can often be difficult to attach four separate bone screws to a single vertebra or other bone, especially where the bone is weak or damaged.
Furthermore, in plate assembly 9 the set screw threaded into bore 4 is openly exposed when plate assembly 9 is implanted within a patient. As such, if the set screw ever becomes loose, it could separate from plate assembly 9 and become a potential hazard to the patient. A second surgical procedure would then be required to retrieve the set screw.
In addition, plate assembly 9 fully covers the bone portions over which plate assembly 9 is placed. For many surgeons this can be problematic in that they want to see portions of the underlying bone(s) or biologic fusion material to ensure that plate assembly 9 is optimally positioned.
Accordingly, what is needed in the art are bone fixation plate assemblies that address some or all of the above shortcomings.